In July 1998, the IEEE standardized OFDM as the basis for a 5 Ghz physical layer (PHY) for wireless local area networks (WLANs). This standard is referred to as IEEE 802.11a and provides for data transmission at rates between 6 and 54 Mbps. This standard is designed for use in Local Area Networks (LANs) to communicate data in a quasi-static indoor environment. That is, although the network's nodes may move about and the environment may change somewhat (for example, by virtue of movement of people and furniture within the range of the network), such movements are quite slow when compared with the packet size used in the OFDM system.
A modification of this standard has been proposed for the Roadside Access (RA) physical layer referred to as 802.11a/RA, with the main difference being a reduction by a factor of two in the serial bit rate for 802.11a/RA. Although the two systems operate in a similar manner, the RA system environment is dramatically different in that it is proposed for use in association with moving automobiles (mobile units) communicating with stationary access points or other mobile units. As currently proposed, 802.11a/RA and similar OFDM systems intended for use in dynamic environments will suffer from errors induced by phase noise and Doppler frequency spreads.